Disclosed herein is a phase inversion emulsification process for controlling latex particle size. More particularly disclosed is a phase inversion emulsification process comprising: a) combining a resin, an organic solvent, an optional neutralizing agent, and a first portion of water in a reactor; wherein said reactor is equipped with a jacket, a vacuum, a condenser connected to the reactor by a distillate conduit, and a receiver connected to the condenser by a condensate conduit, to form a water-in-oil dispersion mixture; b) adding a second portion of water to the reactor to convert the water-in-oil dispersion mixture into an oil-in-water dispersion comprising a latex emulsion of latex particles; c) forming a distillate and controlling the distillate temperature by at least one of: adjusting the jacket temperature, adjusting the vacuum level, or a combination thereof; wherein controlling the distillate temperature controls the particle size change or particle size distribution shift of the latex particles; d) wherein volatile organic compounds are pulled out of the liquid phase in the reactor to a vapor phase and transferred to the condenser via the distillate conduit; e) cooling distillate vapor in the condenser to a liquid phase; and f) collecting the liquid condensate in the receiver.
Phase inversion emulsification (PIE) processes are known. See for example, U. S. Patent Application Publication 2015/0168858, which is hereby incorporated by reference herein in its entirety. U. S. Patent Application Publication 2015/0168858 describes in the Abstract thereof a process for making a latex emulsion suitable for use in a toner composition which applies the model of Brinkman to predict phase inversion point (PIP) during phase inversion emulsification including using this model to calculate the amount of water needed to complete the phase inversion for solvent reuse formulation.
U.S. Pat. No. 9,366,980, which is hereby incorporated by reference herein in its entirety, describes in the Abstract thereof a process for making colored polyester latex by phase inversion emulsification.
U.S. Pat. No. 8,916,320, which is hereby incorporated by reference herein in its entirety, describes in the Abstract thereof a process for making a latex emulsion including contacting at least one amorphous resin with at least two organic solvents to form a resin mixture, adding a neutralizing agent and deionized water to the resin mixture, removing the solvent from the formed latex, and separating the solvent from water. Further, the process is carried out above the resin Tg for making the latex, which drives the latex particle size under 100 nm, where toners made from the latex show improved charging performance. See also U.S. Pat. No. 9,348,248, which is hereby incorporated by reference herein in its entirety.
U.S. Pat. No. 7,713,674, which is hereby incorporated by reference herein in its entirety, describes in the Abstract thereof an emulsion polymerization process comprising polymerizing monomer in an emulsion in a reaction vessel at a first temperature to form a resin; cooling the reaction vessel to a second temperature that is above the softening point of the resin yet below the temperature required for significant depolymerization reaction to occur; and adding water to the cooled reaction vessel in an amount sufficient to effect phase inversion with mixing for a sufficient time to form an aqueous latex emulsion in the absence of a surfactant.
U.S. Pat. No. 9,410,037, which is hereby incorporated by reference herein in its entirety, describes in the Abstract thereof a process for making a crystalline latex suitable for use in a toner by phase inversion emulsification (PIE) where the liquid reagents, such as, organic solvent(s), neutralizing agent and water, are reused from a prior PIE.
U.S. Pat. No. 9,354,531, which is hereby incorporated by reference herein in its entirety, describes in the Abstract thereof a process for making a latex emulsion where distillation occurs at an elevated temperature is used to make resin particles with a conditioned surface which can be used to make magenta toner with increased efficiency.
Latex emulsions of resins may be produced using PIE processes in which resins are dissolved in a mixture of water, a base and organic solvent(s) (e.g., methyl ethyl ketone (MEK), isopropyl alcohol (IPA) or both) to form a water-in-oil (W/O) dispersion (i.e., water droplets dispersed in continuous oil). Subsequently, water is added to convert the dispersion into an oil-in-water (O/W) dispersion. In embodiments, liquids from a prior PIE can be reused in a subsequent PIE.
As described above, phase inversion emulsification (PIE) processes for making resin latex from a resin use solvents such as methyl ethyl ketone (MEK) and isopropyl alcohol (IPA) to dissolve the resin. After conversion, the volatile organic compounds (VOCs) need to be removed from the latex in order to meet environmental regulations for use as a raw material in both the emulsion aggregation (EA) process and the toner end product. The current method of solvent removal is vacuum distillation of the latex.
In order for the latex to be a useful raw material in the EA process, the particle size distribution needs to be in a specified range. The PIE formulation is always pre-tested and modified in lab to adjust latex particle size to desired specifications due to lot-to-lot variation of resin properties. This is the only way for particle size control in current latex production. However, this formulation adjustment only ensures the particle size after phase inversion. Particle size variability can still be observed due to solvent stripping. In particular, as the VOCs are removed from the emulsion, the size of the particles shrinks, often leading to variability and risk of producing particle out of specifications. Currently, the method to predict the degree of shrinkage is to take the latex sample before distillation and mix it with 50° C. water. By adding the latex to the higher temperature water, the particle will show similar behavior of shrinking that is seen during distillation but it does not always reflect the final particle size after distillation. This comparison is then used to modify the PIE formulation to give a desired final result. However, it is not a direct comparison and the shrinking that is seen during distillation is not always consistent making this method unreliable.
As described above, the current method to predict the degree of shrinkage of distilled latex particle is to add the latex sample to 50° C. water and then measure the particle size distribution. The 50° C. water facilitates the evaporation of solvents from the latex particle, simulating the shrinking process in latex distillation. This method allows for an estimation of the change of particle size after stripping. However, it does not provide a method for size control of the distilled latex. Further, the simulated particle does not always reflect the actual final particle after distillation.
Currently available latex processes are suitable for their intended purposes. However a need remains for improved latex processes. Further, a need remains for a reliable method to control the latex particle size shift so that a higher quality of latex can be produced, in embodiments for toner EA processes.
The appropriate components and process aspects of the each of the foregoing U.S. Patents and Patent Publications may be selected for the present disclosure in embodiments thereof. Further, throughout this application, various publications, patents, and published patent applications are referred to by an identifying citation. The disclosures of the publications, patents, and published patent applications referenced in this application are hereby incorporated by reference into the present disclosure to more fully describe the state of the art to which this invention pertains.